TYPES OF HUMAN CELL
The cells that make up the nervous system and the brain are nerve cells or neurons. Electrical messages pass between nerve cells along long filaments called axons. To cross the gaps between nerve cells (the synapse) that electrical signal is converted into a chemical signal. These cells enable us to feel sensations, such as pain, and they also enable us to move.
The cells that make up bone matrix – the hard structure that makes bones strong – consist of three main types. Your bone mass is constantly changing and reforming and each of the three bone cells plays its part in this process. First the osteoblasts, which come from bone marrow, build up bone mass and structure. These cells then become buried in the matrix at which point they become known as osteocytes. Osteocytes make up around 90 per cent of the cells in your skeleton and are responsible for maintaining the bone material. Finally, while the osteoblasts add to bone mass, osteoclasts are the cells capable of dissolving bone and changing its mass.
The cones and rods on the retina at the back of the eye are known as photoreceptor cells. These contain light- sensitive pigments that convert the image that enters the eye into nerve signals, which the brain interprets as pictures. The rods enable you to perceive light, dark and movement, while the cones bring colour to your world.
The cells in your liver are responsible for regulating the composition of your blood. These cells filter out toxins as well as controlling fat, sugar and amino acid levels. Around 80 per cent of the liver’s mass consists of hepatocytes, which are the liver’s specialised cells that are involved with the production of proteins and bile.
Therearethreetypes of muscle cell – skeletal, cardiac and smooth–and eachdiffers depending onthefunction it performs and its location inthe body. Skeletal muscles contain long fibres thatattach to bone. When triggered by anervesignal, the muscle contracts and pulls thebone withit, making you move. Wecan control skeletal muscles because they are voluntary. Cardiac muscles, meanwhile, areinvoluntary, whichis fortunate because they areused to keep your heart beating. Found in thewalls of theheart, these muscles createtheir own stimuli to contract without input from the brain. Smooth muscles, whicharepretty slowand also involuntary, makeup the linings of hollow structures suchas blood vessels and your digestive tract. Their wave-likecontraction aids the transport of blood around thebody and the digestion of food.
These cells – also known as adipocytes or lipocytes – make up your adipose tissue, or body fat, which can cushion, insulate and protect the body. This tissue is found beneath your skin and also surrounding your other organs. The size of a fat cell can increase or decrease depending on the amount of energy it stores. If we gain weight the cells fill with more watery fat, and eventually the number of fat cells will begin to increase. There are two types of adipose tissue: white and brown. The white adipose tissue stores energy and insulates the body by maintaining body heat. The brown adipose tissue, on the other hand, can actually create heat and isn’t burned for energy – this is why animals are able to hibernate for months on end without food.
Epithelial cells make up the epithelial tissue that lines and protects your organs and constitute the primary material of your skin. These tissues form a barrier between the precious organs and unwanted pathogens or other fluids. As well as covering your skin, you’ll find epithelial cells inside your nose, around your lungs and in your mouth.
RED BLOOD CELLS
Unlike all theother cells in your body, your red blood cells (also known as erythrocytes) do not contain a nucleus. You aretopped up with around 25 trillion red blood cells – that’s a third of all your cells, making them the most common cell in your body. Formed in the bonemarrow, these cells are important because they carry oxygen to all thetissues in your body. Oxygen is carried in haemoglobin, apigmented protein that gives blood cells their red colour.